1. Field of the Invention
The present invention relates generally to computer software and more particularly to software compilers.
2. Description of the Background Art
At present, there are two common steps involved in constructing an application that will run on a computer. The first step is the compilation phase that accomplishes a translation of the source code to a set of object files written in machine language. The second step is the link phase that combines the set of object files into an executable object code file.
Today, most modern programming languages support the concept of separate compilation, wherein a single computer source code listing is broken up into separate modules that can be fed individually to the language translator that generates the machine code. This separation action allows better management of the program's source code and allows faster compilation of the program.
The use of modules during the compilation process enables substantial savings in required memory in the computer on which the compiler executes. However, such use limits the level of application performance achieved by the compiler. For instance, optimization actions that are taken by a compiler are generally restricted to procedures contained within a module, with the module barrier limiting the access of the compiler to other procedures in other modules. This limitation is of significance when attempting to accomplish inlining. Inlining replaces a call site with the called routine's code. In-line substitution eliminates call overhead and tailors the call to the particular set of arguments passed at a given call site. It increases the context for subsequent scalar optimizations and instruction scheduling, thus improving run-time performance in general. Cross-module inlining is a technique to substitute a call site by the called routine's code even when the call site and the called routine reside in different modules.
The modular handling of routines by the compiler creates a barrier across which information, which could be of use to the compiler, is invisible. It has been recognized in the prior art that making cross-modular information available during the compilation action will improve application performance. Thus, a compiler that can see across modular barriers (a cross-module optimizing compiler) can achieve significant benefits of inter-procedural optimization and achieve noticeable gains in performance of the resulting application. There has been prior work showing the run-time performance potential of cross-file optimizations. For example, “Scalable Cross-Module Optimization”, described by A. Ayers, S. de Jong, J. Peyton, and R. Schooler, reports performance speedups of as much as 71%. “Aggressive inlining”, described by A. Ayers, R. Gottlieb, and R. Schooler, reports significant performance speedups by performing cross-file inlining.